A flood is when land that is usually dry is submerged by an overflow of water. There are five different types of flooding and they are aerial, catastrophic, coastal, riverine and urban flooding. Aerial flooding is caused by heavy rainfall or snowmelt. Catastrophic flooding is caused by infrastructure failure, like the failure of a levee or dam. Flooding is caused by rising sea levels, like a storm surge caused by a hurricane. Damage caused by flooding can reach into the billions of dollars. Around 90% of all the natural disaster declarations in the United States are related to some sort of flooding. The deadliest flood on record was the 1939 China floods, also known as the 1931 Yangtze-Huai River floods. Some estimates have the death toll as high as four million people. This flood is also considered the deadliest natural disaster in recorded history. A flood is an overflow of water that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrology and are of significant concern in agriculture, civil engineering and public health. Human changes to the environment often increase the intensity and frequency of flooding, for example land use changes such as deforestation and removal of wetlands, changes in waterway course such as with levees, and larger environmental issues such as climate change and sea level rise.

Flood